The proposed research focuses on the assessment of the ability of 2 larval control agents, Bacillus sphaericus (Bs) and B. thuringiensis var. israelensis (Bti) (VectoLex(r) and Vectobac(r), Valent Biosciences, USA) to reduce clinical malaria in children. Effective malaria control is under threat from drug and insecticide resistance in different parts of the tropics, and larval control may offer a new alternative for effective control. Larval control has been historically successful, but has been largely neglected over the last 50 years. Promising new formulations of Bs and Bti have recently been shown to give excellent control of the major vectors of malaria in Africa. Use of these products is better than chemical larvicides since they have multiple actions and do not appear to elicit the evolution of resistance when used together. To date few trials have measured the clinical impact of larviciding with Bs and Bti and these have been hampered by small sample size within clusters and a lack of replication of clusters and hence, low statistical power. A larger intervention study with replication is urgently required to demonstrate the proof of concept that larval control is an effective malaria control tool and to allow informed decision making by international policy makers of the relative merits of larval control. We therefore propose to carry out a large cluster-randomised intervention trial in The Gambia to investigate the ability of larval control to reduce malaria morbidity in children. The results from this study will make a major contribution to quantifying the importance of the use of Bs and Bti in the fight against malaria.